It is known to use a handpiece, e.g. in combination with a scanning device, for tissue treatment, such as described in U.S. Pat. No. 6,190,376, U.S. Pat. No. 6,074,382, and in U.S. Pat. No. 6,383,177 hereby incorporated by reference. However, in known handpieces the components constituting the handpiece, such as optical components, are ‘fixed’, i.e. they are impossible or at least very difficult to exchange for other components. Therefore, the known handpieces are designed for specific purposes or specific kinds of treatment, and/or to be used in combination with specific light sources. Thus, they are relatively inflexible and not easily adapted to other purposes or light sources than those they were originally designed to.